1. Related Technical Fields
Related technical fields include map information distribution systems and centers. Specifically, related technical fields include map information distribution systems and centers that distribute updating information for updating map information to a navigation device.
2. Related Art
In recent years, more vehicles have been equipped with a navigation device that provides driving guidance to a driver to reach the desired destination easily. Such devices detect the current vehicle position by a GPS receiver and such, obtain map data corresponding to the current position from recording media such as DVD-ROM and HDD or via a network, and display the map data on a liquid crystal monitor. The navigation device makes it possible to understand where the vehicle is currently driving at a glance by displaying a map image of a neighboring area of the current vehicle position based on the map data on a display, as well as displaying a vehicle position mark superimposed on the map image and scrolling the map image according to the movement of the vehicle or moving the vehicle position mark while fixing the map image on the screen.
Every year, new roads (newly constructed roads) are constructed. With the construction of new roads, existing roads may be removed or the configuration of existing roads may be modified. Therefore, the map data stored in a navigation device needs to be updated at some interval. Updating map data is done by, for example, replacing an old DVD with a new DVD, loading updated map information into the hard disk at shops, or renewing the content of the hard disk based on map data distributed from a map information distribution center, etc.
Various map information distribution centers which automatically distribute the updating information for updating map data stored in a navigation device to the aforementioned navigation device have been offered.
For example, when a navigation device requests differential data for updating map information from a map information distribution center, the navigation device transmits a navigation ID that identifies the navigation device and a mesh number for updating map information. The map information distribution center compares a version of map information of the mesh stored in the navigation device with that of the latest version based on the navigation ID and mesh number received and, when differential data is available, transmits the differential data to the navigation device. Such a map information distribution center is disclosed in Japanese Patent Application Publication No. JP-A-2004-125510 (see, e.g., paragraphs [0032]-[0040] and [0046]-[0063], and FIGS. 15-18 and 20-29.